1. Field of the Invention
The present invention relates to a driving method of a plasma display panel and, particularly, to a driving method of a plasma display panel, which performs a matrix display of an A.C. discharge type.
2. Description of Related Art
In general, the plasma display panel (referred to as xe2x80x9cPDPxe2x80x9d, hereinafter) has several advantageous features. That is, for example, the PDP has a thin structure and a large contrast ratio of display without flicker. Further, the PDP allows a screen size to be made relatively large and its response speed is high. In addition, the PDP emits light spontaneously and is capable of emitting multi-color light by utilizing suitable fluorescent materials. Therefore, the PDP has been becoming more popular in the fields of display related to computers and color picture displays, etc.
Depending upon the operating system of the PDP, the driving method of such PDP is roughly classified to an A.C. discharge type and a D.C. discharge type. In the A.C. discharge type PDP, a dielectric member covers electrodes and the PDP is operated indirectly in an A.C. discharge state. In the D.C. discharge type PDP, electrodes are exposed to a discharge space and the PDP is operated in a D.C. discharge state. The A.C. discharge type PDP is further classified to those of a memory operating type, which utilizes memories of discharge cells as its driving system, and a refresh operating type, in which discharge cell memories are not utilized. Incidentally, luminance of the PDP is proportional to the number of discharges, that is, the repetitive number of pulse voltage. In the case of the above mentioned refresh type PDP, the larger the display capacity provides the lower the luminance. Therefore, PDP of the refresh operation type is mainly used for those having small display capacity.
FIG. 1 is a perspective view of an example of a construction of one of display cells 16 of the A.C. discharge, memory operation type PDP in a disassembled state. The display cell 16 is composed of a front and rear insulating substrates 1 and 2 both formed of glass material, a transparent scan electrode 3 formed on a lower surface of the insulating substrate 2, a transparent sustaining electrode 4 also formed on the lower surface of the insulating substrate 2, trace electrodes 5 and 6 arranged on the scan electrode 3 and the sustaining electrode 4, respectively, in order to reduce electrode resistance thereof, a data electrode 7 formed on an upper surface of the insulating substrate 1 and extending perpendicularly to both the scan electrode 3 and the sustaining electrode 4, a discharge gas space 8 defined by the insulating substrates 1 and 2 and partition walls 9, which define the display cell, and filled with discharge gas such as helium, neon or xenon or a mixture thereof, a fluorescent material 11 for converting ultra-violet ray generated by discharge of the discharge gas into a visible light 10, a dielectric member 12 covering the scan electrode 3 and the sustaining electrode 4, a protective layer 13 of such as magnesium oxide for protecting the dielectric member 12 against discharge and a dielectric member 14 covering the data electrode 7.
Describing a discharge operation of the selected one of the display cells 16 shown in FIG. 1, when discharge of gas in the discharge gas space 8 is started by applying a pulse voltage exceeding a discharge threshold value of discharge gas between the scan electrode 3 and the data electrode 7, positive and negative charges are attracted to surfaces of the oppositely arranged dielectric members 12 and 14, respectively, correspondingly to the polarity of the pulse voltage and accumulated thereon. An equivalent internal voltage caused by the accumulated electric charges, that is, a wall voltage, is opposite in polarity to the applied pulse voltage. Therefore, an effective voltage inside the display cell is lowered with growth of the discharge, so that it becomes impossible to sustain the discharge and the discharge is terminated even if the applied pulse voltage is held at a constant value. When a sustaining pulse voltage, which is the same in polarity as the wall voltage, is applied between the scan electrode 3 and the sustaining electrode 4, a portion of the sustaining pulse voltage, which corresponds to the wall voltage, is overlapped as an effective voltage. Therefore, it is possible to provide discharge with a discharge voltage exceeding the discharge threshold value even if a voltage level of the sustaining pulse is low. As a consequence of this fact, it becomes possible to sustain the discharge by continuously applying the sustaining pulse voltage across the scan electrode 3 and the sustaining electrode 4. This function is the memory operation of the A.C. discharge type PDP mentioned previously. Applying a wide and low voltage pulse or an erase pulse, which can neutralize the wall voltage, to the scan electrode 3 or the sustaining electrode 4, can terminate the above sustaining discharge. The erase pulse may be a narrow pulse having a voltage amplitude as small as that of the sustaining pulse.
FIG. 2 is a plan view schematically showing a PDP 15 formed by arranging the display cells 16 each shown in FIG. 1 in matrix. In FIG. 2, the PDP 15 takes in the form of a panel constituted by arranging the display cells 16 in a matrix of n rows and m columns. The PDP 15 includes scan electrodes Sw1, Sw2, . . . , Swn and sustaining electrodes Su1, Su2, . . . , Sun, which are arranged in parallel to each other, as the row electrodes and data electrodes D1, D2, . . . , Dm, which are orthogonal to the scan electrodes and the sustaining electrodes, as the column electrodes.
FIG. 3 shows driving pulse waveforms for illustrating a conventional drive method of the PDP shown in FIGS. 1 and 2. This driving method is equivalent to that proposed in xe2x80x9cSociety for Information Display International Symposium Digest of Technical Papersxe2x80x9d, Vol. XXVI (pp. 807-810) and this driving method will be referred to as xe2x80x9cfirst prior art examplexe2x80x9d, hereinafter.
In FIG. 3, Wu depicts a waveform of a sustaining electrode driving pulse, which is commonly applied to the sustaining electrodes Su1, Su2, . . . , Sun, Ws1, Ws2, . . . , Wsn depict waveforms of scan electrode driving pulses applied to the respective scan electrodes Sw1, Sw2, . . . , Swn, respectively, and Wd depicts a waveform of a data electrode driving pulse selectively applied to one of the data electrode Di (1xe2x89xa6ixe2x89xa6m). One driving period (1 frame) is constituted with a pre-discharge period A, a write discharge period B and a sustaining discharge period C and a desired image display is obtained by repeating this driving period.
The pre-discharge period A is provided in order to produce active charges particles and wall charges in the discharge gas space to thereby obtain a stable write discharge characteristics in the write discharge period B. In the pre-discharge period A, a pre-discharge pulse Pp for preliminarily discharging all display cells of the PDP 15 is applied to all of the sustaining electrodes and then a pre-discharge erase pulse Ppe for extinguishing electric charges among the wall charges produced in the pre-discharge period A, which block the write discharge and the sustaining discharge, is applied to all of the respective scan electrodes, simultaneously. That is, the discharge is produced in all of the display cells by applying the pre-discharge pulse Pp to the sustaining electrodes Su1, Su2, . . . , Sun, first, and, thereafter, the erase discharge is produced by applying the erase pulse Ppe to the scan electrodes Sw1, Sw2, . . . , Swn to erase the wall charges accumulated by the pre-discharge pulse Pp.
A scan base pulse Pbw is commonly applied to the respective scan electrodes Sw1, Sw2, . . . , Swn throughout the write discharge period B. Further, in the write discharge period B, a sequentially scan pulse Pw is sequentially supplied to the scan electrodes and a data pulse Pd is selectively supplied to the data electrode Di (1xe2x89xa6ixe2x89xa6m) of the display cell to be displayed, in synchronism with the application of the scan pulse Pw, to produce a write discharge in the display cell to thereby produce the wall charges.
The scan base pulse Pbw commonly applied to the scan electrodes throughout the write period B is used to prevent the wall charges necessary for shifting the write discharge to the sustaining discharge from being lost due to an erase discharge, which is produced by the internal voltage of the display cell due to the wall charges and the large amount of active charged particles existing within the space at a time when the scan pulse Pw and the data pulse Pd disappear.
In the sustaining discharge period C, sustaining discharge necessary to obtain a desired brightness of the display cells, which perform the write discharge in the write discharge period B, is sustained by applying a first sustaining pulse Pu to the sustaining electrodes and applying a second sustaining pulse Ps having a phase delayed from the sustaining pulse Pu by 180xc2x0 to the scan electrodes.
Since, in the PDP driving system shown as the first prior art example, the pre-discharge period, the write discharge period and the sustaining discharge period are completely separated in time from each other, a time from the pre-discharge to the write discharge is different from a time from the write discharge to the sustaining discharge every scan line. Therefore, for first scan lines closest in time to the pre-discharge, an attenuation of the space charge after the preparatory discharge is distinguished is small and, therefore, the write discharge occurs easily. However, since the time from the write discharge to the sustaining discharge is relatively long, there is a problem that the wall charge produced by the write discharge is reduced gradually before the sustaining discharge is started, so that the smoothness of transition from the write discharge to the sustaining discharge is degraded. On the contrary, for subsequent scan lines, the time from the write discharge to the sustaining discharge is relatively short and, therefore, there is substantially no degradation of the smoothness of transition from the write discharge to the sustaining discharge due to extinction of the wall charge produced by the write discharge. However, there is another problem that, since the time from the pre-discharge to the write discharge is long, the attenuation of the space charge after the pre-discharge is distinguished is considerable and the write discharge can not occur easily.
An object of the present invention is to provide a stable driving method of an A.C. discharge type PDP of matrix type.
Another object of the present invention is to provide a stable driving method of an A.C. discharge type PDP of matrix type, in which a transition from a write discharge to a sustaining discharge is improved by enhancing and stabilizing the write discharge by applying an auxiliary scan pulse opposite in polarity to a scan pulse to display cells of the PDP immediately before the scan pulse is applied thereto and by applying a first sustaining pulse immediately after the write discharge and sustaining it until a second sustaining pulse is started.
A further object of the present invention is to realize a display device having a large display capacity by providing a driving method of an A.C. discharge type PDP of matrix type, in which an auxiliary scan pulse opposite in polarity to a scan pulse to scan electrodes immediately before the scan pulse is applied to the scan electrodes to produce a state in which gas discharge can be easily produced, that is, a state in which a probability of occurrence of a write discharge is high, to thereby reduce a variation of discharge delay time and to shorten a time necessary for a write of respective scan lines, so that it becomes possible to drive a larger number of scan lines within a constant time.
Another object of the present invention is to widen a driving voltage range of an A.C. discharge type PDP of matrix type by providing a driving method thereof, in which a sustaining pulse immediately after the write discharge is applied to the scan electrode and the sustaining pulse is sustained till a time close to a start time of a next sustaining pulse, to smooth transition from the write discharge to a first sustaining discharge and transition from the first sustaining discharge to a second sustaining discharge, to thereby make possible to start the sustaining discharge even with a low sustaining voltage.
According to a first aspect of the present invention, a driving method of an A.C. discharge type PDP of a matrix type, which is constructed with a plurality of display cells including a plurality of row electrode pairs each including a scan electrode and a sustaining electrode and a plurality of data electrodes arranged in a direction orthogonal to the row electrode pairs and constituting column electrodes, comprises the steps of applying, in a pre-discharge period, a pre-discharge pulse to the scan electrodes and the sustaining electrodes simultaneously in a pre-discharge period, supplying an erase pulse for erasing wall charges accumulated by the pre-discharge pulse to the respective sustaining electrodes to produce an erase discharge, in a write discharge period, sequentially applying an auxiliary scan pulse opposite in polarity to the scan pulse to the scan electrodes immediately before an application of a sequential scan pulse to the respective scan electrodes, applying the scan pulse to the respective scan electrodes sequentially and applying a data pulse to the data electrodes selectively in synchronism with the scan pulse.
By sequentially supplying the auxiliary scan pulse opposite in polarity to the scan pulse to the scan electrodes immediately before the application of the sequential scan pulse to the respective scan electrodes, space charges, which are the same in polarity to a write voltage, are attracted such that an electric field in the display cell is cancelled out. Therefore, the electric field in the display cell is further increased when the scan pulse is supplied thereto, so that it is possible to produce a state in which the write discharge is easily produced. Consequently, the stability of the write discharge is improved.
According to a second aspect of the present invention, a driving method of an A.C. discharge type PDP of matrix type comprises, in the write discharge period, the steps of sequentially applying a scan pulse to the respective scan electrodes, applying a first sustaining pulse and an opposite sustaining pulse opposite in polarity to the first sustaining pulse to the scan electrodes and the sustaining electrode, respectively, immediately after the application of the scan pulse to the scan electrodes and sustaining these sustaining pulses till a time close to an application of a second sustaining pulse. According to this method, since the application of the sustaining pulse is started while the wall charges and the space charges provided by the write discharge are not extinguished substantially, the transition from the write discharge to the first sustaining discharge during the sustaining discharge period becomes improved.
According to a third aspect of the present invention, the first and second driving methods are combined in order to stabilize the write discharge by means of an auxiliary scan pulse and to make the transition from the write discharge to the sustaining discharge smooth by means of the sustaining pulse applied immediately after the application of the scan pulse, to thereby obtain a more stable driving of the PDP.